The present invention relates to a connecting structure and a connecting method of a terminal fitting and an electric wire in which a terminal is caulked and connected to a core wire portion of an electric wire by swaging, while forming a male contact portion on the terminal.
FIGS. 9 and 10 show a configuration of a related connecting structure and a connecting method of a terminal fitting and an electric wire as disclosed in Japanese Utility Model Publication No. 48-32885U.
In FIG. 9, the reference numeral 41 denotes a male terminal formed of a copper alloy, the reference numeral 42 denotes a sheathed electric wire which exposes a core wire portion 43 formed of aluminum or an aluminum alloy, and the reference numeral 44 denotes a relay terminal for connecting the male terminal 41 to the core wire portion (core wire portion) 43. The relay terminal 44 is formed of the same aluminum material as that of the core wire portion 43, that is, aluminum or an aluminum alloy.
The male terminal 41 is provided with a plate-shaped contact portion 48 having such a shape as to be similar to that of an LA terminal based on JIS, that is, a ring terminal for an automobile on one of ends and an uneven shaft portion 45 on the other end. The relay terminal 44 has hole portions 46 and 47 on both front and rear sides, and the shaft portion 45 of the male terminal 41 is inserted in the hole portion 46 on the front side, and the outside part of the hole portion 46 is caulked by a proper tool (not shown) so that the male terminal 41 is connected to the relay terminal 44 as shown in FIG. 10.
Moreover, the core wire portion 43 of the electric wire 42 is inserted into the hole portion 47 on the rear side and the outside part of the hole portion 47 is caulked by a proper tool (not shown) so that the electric wire 42 is connected to the relay terminal 44. Consequently, the electric wire 42 and the male terminal 41 are electrically connected through the relay terminal 44.
Although the core wire portion 43 formed of the aluminum material has a poorer conductivity than that of the core wire portion formed of copper, it is light-weighted and inexpensive. In addition, if a diameter thereof is increased, a corona characteristic can be improved. Therefore, the core wire portion 43 can meet a requirement for a multi-source and a large current and is suitable for an electric car, for example.
In the structure shown in FIG. 10, the male terminal 41 formed of copper having a greater elastic modulus than that of the relay terminal 44 formed of aluminum is used. Consequently, the caulked shaft portion 45 comes in close contact with the inner periphery of the hole portion 46 (FIG. 9) so that an excellent electrical contact property can be obtained. Moreover, the relay terminal 44 and the core wire portion 43 which are formed of the same material are caulked so that an connecting portion can be prevented from being loosened due to a difference in the elastic modulus.
As a matter of course, the materials of the relay terminal 44 and the core wire portion 43 having the configuration described above are not limited to aluminum but copper or a copper alloy can also be used for formation.
In the related connecting structure and connecting method of a terminal and an electric wire, however, the relay terminal 44 is used so that the number of parts is increased. Consequently, there is a problem in that a cost is increased. Moreover, the male terminal 41 and the relay terminal 44 are caulked and connected while the relay terminal 44 and the electric wire 42 are caulked and connected so that a time and labor to be taken is doubled. Thus, there is a problem in that a connecting workability is poor.
Moreover, there are two front and rear connecting portions, that is, the connection of the male terminal 41 to the relay terminal 44 and the connection of the relay terminal 44 to the electric wire 42. Therefore, a contact resistance might be increased so that a conduction performance might be deteriorated.
When the caulking operation is performed, a clearance is easily formed between the shaft portion 45 and the relay terminal 44 and between the relay terminal 44 and the core wire portion 43, and a clearance is easily formed between wires constituting the core wire portion 43. Consequently, there is a probability that the conduction performance might be deteriorated.
In particular, the core wire portion 43 and the relay terminal 44 which are formed of the aluminum material are used. Therefore, in the case in which the clearance is formed, the inner face of the hole portion 46 of the relay terminal 44 connecting the male terminal 41, the face of the core wire portion 43 and the inner face of the hole portion 47 of the relay terminal 44 are oxidized with the passage of time so that an oxide film is formed. Consequently, the contact resistance of the male terminal 41 and the core wire portion 43 might be increased so that the conduction performance is deteriorated.
It is therefore an object of the present invention to provide a connecting structure and a connecting method of a terminal and an electric wire, wherein a male terminal and a core wire portion of an electric wire can be easily connected in a short time at a low cost with a high workability; the male terminal and the core wire portion of the electric wire can be reliably connected without a clearance to enhance a conduction performance; and the problem of an oxide film can be eliminated to attain the object easily and reliably even if a terminal and a core wire portion are formed of an aluminum material.
In order to achieve the above object, according to the present invention, there is provided a connecting structure, comprising:
an electric wire in which a core wire is covered with an insulation sheath; and
a cylindrical terminal fitting, integrally formed with a male type contact portion at a front end portion thereof by rotary swaging, the terminal fitting including a connecting portion which is electrically connected to the electric wire such that at least a part of the core wire is caulked uniformly over a whole periphery thereof by rotary swaging.
According to the present invention, there is also provided a method of manufacturing a terminal fitting electrically connected with an electric wire in which a core wire is covered with an insulating sheath, comprising the steps of:
providing a cylindrical conductive member formed with a through hole;
inserting at least a part of the core wire of the electric wire into the through hole from a first end of the cylindrical member;
performing rotary swaging onto at least the first end of the cylindrical member so as to caulk the inserted portion of the electric wire uniformly over a whole periphery thereof; and
performing rotary swaging onto at least a second end of the cylindrical member so as to compress radially to form a male type contact portion thereat.
In the above configurations, since the connecting portion of the terminal fitting is uniformly compressed and plastically deformed over the whole periphery by the rotary swaging (the whole peripheral face of the connecting portion is uniformly caulked), the inner face of the connecting portion comes in close contact with the core wire of the electric wire without a clearance. Further, since the core wire is strongly compressed in a central direction over the whole periphery by the rotary swaging, a clearance between a plurality of strand wires constituting the core wire is eliminated so that the conduction resistance of the electric wire and the terminal fitting can be reduced and the conduction performance can be enhanced.
Moreover, the male type contact portion is formed simultaneously or almost simultaneously at the same step as the formation of the connecting portion by the rotary swaging. Consequently, a time required for manufacturing the terminal can be shortened and the cost of the terminal can be reduced. Furthermore, since another member such as a relay terminal is not required, the cost of parts can be reduced and the man-hour of the electric wire connection can be reduced. Moreover, since the alignment of centers of the contact portion and the connecting portion is automatically completed, the adhesion of a waterproof rubber plug to be inserted and fixed into the outer periphery of the electric wire and the internal wall face of the terminal housing chamber of a connector housing can be enhanced, for example. Furthermore, the section of the male contact portion is formed to be completely circular (completely round) so that the contact property of a mating female terminal and the contact portion can be enhanced.
Preferably, the terminal fitting is formed with an annular flange portion on an outer periphery thereof.
In this configuration, a portion which is not subjected to the rotary swaging is provided in a part of the terminal fitting. Consequently, the annular flange portion can be formed easily at a low cost. The flange portion is useful for engaging or fixing the terminal to a connector housing, for example.
Preferably, at least one of the terminal fitting and the core wire is made of an aluminum material.
In this configuration, force required for plastically processing the contact portion is not greater as compared with a copper material and the processing can be carried out easily and rapidly. Even in such a case, since the inner face of the connecting portion of the terminal fitting comes in close contact with the core wire of the electric wire without clearance, an oxide film can be prevented from being formed on the inner face of the terminal fitting or the core wire with the passage of time. Thus, an excellent conduction performance can be maintained. Furthermore, the core wire eats into the inner peripheral face of the terminal by the rotary swaging so that an initial oxide film can be removed by friction and an excellent conduction performance can be obtained.
Preferably, the rotary swaging for caulking and the rotary swaging for forming the contact portion are performed by a first die having a first curvature for caulking and a second die having a second curvature for the contact portion formation.
In this configuration, the connecting portion and the contact portion can be efficiently compressed in a short time and the connection of the electric wire and the formation of the male terminal can be efficiently carried out.
Here, it is preferable that the manufacturing method further comprises the step of performing rotary swaging for forming a slanted portion which connects the caulked portion of the cylindrical member and the male type contact portion, by using a third die for forming the slanted portion.
In this configuration, the slanted portion between the contact portion and the connecting portion is compressed to be well tapered so that a commercial value can be enhanced. In addition, the bending strength of the contact portion can be increased so that deformation can be prevented from being caused by an interference during insertion to a female terminal on the other side.
Alternatively, the rotary swaging for caulking and the rotary swaging for forming the contact portion are performed by a single die having a first curvature portion for caulking and a second curvature portion for the contact portion formation.
In this configuration, the step of exchanging the dies is not required so that a processing work efficiency can be enhanced still more.
Here, it is preferable that the manufacturing method further comprises the step of performing rotary swaging for forming a slanted portion which connects the caulked portion of the cylindrical member and the male type contact portion. The single die has a portion for forming the slanted portion.
In this configuration, the die for processing the contact portion and for processing the connecting portion serves as the slanted portion of the terminal fitting. Consequently, the step of exchanging the dies is not required so that the processing work efficiency can be enhanced still more.